Abstract. Silt in some areas of our country is very extensive, its distribution is different from the cohesive soil, or sand soil, has unique engineering characteristic. Silt regional characteristics make it has many unique physic-mechanical performance. This article take the G209 (Inner Mongolia Helin to Qingshuihe section) the roadbed silty soil as the study object, study its basic physics, the mechanical properties as well as the distortion and the intensity change rule under the dry-wet circulation, do a comprehensive and systematic analysis about varieties of basic engineering characteristic of the silt in the region Through the condition of dry-wet circulation of unconsolidated tri-axial tests, this article study the silt sample failure pattern under different degree of compaction, stress-strain relations and the change rule of strength. The test results show that: as cycle index less and confining pressure down, test sample is basically brittle failure, on the contrary case, it is behaved for plastic failure and stress-strain curve is close to sclerosis type; When cycle index increase gradually, the cohesion of silt reduced significantly ,with the increase of dry-wet circulation times internal friction angle is on the trend of the attenuation oscillation ; On this basis, we build the relationship expression of shear strength parameters cohesion internal friction angle and dry-wet circulation times.